A three-port nonreciprocal device includes: a carrier plate; a ferrite substrate provided on this carrier plate; a Y junction-shaped line provided on the ferrite substrate; a spacer provided on this line; and a permanent magnet provided on this spacer.
In some cases, multiple three-port nonreciprocal devices are connected together for increasing the number of ports to four or more. For example, a conventional four-port nonreciprocal device includes two three-port nonreciprocal devices which are connected together in series on the same surface of a carrier plate (see the description of U.S. Pat. No. 7,772,937).
Because the volume of the permanent magnet used in each nonreciprocal device is large, the packaging area of the three-port nonreciprocal device is large. For this reason, a four-port circulator needs twice as large a part-packaging area as a three-port circulator does. This increases the area of a packaging substrate.
Against this background, there have been demands for a multi-port nonreciprocal device which does not entail the increase in the packaging area.